About 50% of the world's population, 90% of rural households in developing countries and 78% of Sri Lankan households rely on solid fuel for cooking. Incomplete combustion of solid fuel is the major contributor to indoor air pollution (IAP) in developing countries. Globally, about 910,000 acute lower respiratory infection (ALRI) deaths among d 5 year children can be attributed to IAP. The main type of solid fuel in Sri Lanka is biomass. Particulate Matter (PM) released from burning of biomass fuel is known to be hazardous to human health particularly to the respiratory system. Studies have suggested that black carbon (BC), a component of PM, may be primarily responsible for health effects. BC is also the second-largest contributor to global warming. Approximately 20% of global BC is emitted from household biomass fuel use. Longitudinal studies of PM2.5 from biomass fuel and adverse respiratory health effects of younger children are limited; while studies on BC from biomass fuel use and adverse respiratory health effects are even more scarce. The proposed prospective cohort study aims to evaluate the relationship between exposure to PM2.5 and BC and respiratory health outcomes among children below two years of age. The study will be conducted in a low traffic exposure area of the Kalutara Medical Officer of Health (MOH) area in Sri Lanka. Our research strategy is to follow-up 475 children from birth to their second birthdays to assess exposure to IAP and respiratory health. PM2.5 and BC exposure will be measured in the households of 25% of children, twice yearly for two years. These exposure measurements will be used to estimate exposure for children in the remaining households without monitoring data. Respiratory health of children from day of birth until the second birthday will be ascertained using an array of sources some of which include community health workers' assessments and physicians' diagnosis. Information on covariates will come from questionnaires and from data maintained by the Sri Lankan primary health care system. This project provides an opportunity to address crucial knowledge gaps pertaining to PM2.5 and BC and respiratory health, while strengthening Sri Lanka's IAP research capacity. In doing so, the project will provide the evidence that may be translated into practice and policy for IAP exposure reduction in the country with extension of the benefits to include climate change mitigation.